1. Field of the Invention
The present invention relates to a flying head assembly for a magneto-optical recording drive. More particularly, the invention relates to an improved flying head assembly which can form a vertical magnetic field directed towards the focusing plane of an optical recording medium efficiently.
2. Discussion of the Related Art
To describe the principle of recording by this type of magneto-optical recording drive, referring to FIG. 17, a recording layer (a) comprised of a magnetic material is irradiated with a laser spot while a magnetic field is imposed in the direction indicated by the arrows. The Kerr rotation angle at the site of irradiation is changed through reversal of the direction of the magnetic field at this site, and such changes of the Kerr rotation angle are used to effect recording and playback of information (see FIG. 18). The system is further one in which, as illustrated in FIG. 19, recording sites of the recording layer (a) are irradiated with a laser spot while the direction of magnetization is made the reverse of what it was at the time of recording, thereby returning the direction of the magnetic field at the irradiated sites to their pre-recording states and erasing information.
The flying head described in Japanese Patent Publication No. 60-261052 is known as an optical head for effecting recording, playback and erasure of information in such a magneto-optical recording drive.
As shown in FIGS. 20-22, the main elements of this flying head (b) are an air slider (b1) which is made of soft magnetic material and is floated by the air stream that accompanies rotation of an optical recording medium (c), a prism (b2) which is mounted on the air slider (b1) and by which laser light from a light source (d) such as a semiconductor laser, etc. is reflected towards the optical recording medium (c), an object lens (b4) which is mounted in a light path opening portion (b3) of the air slider (b1) and by which the laser light reflected by the prism (b2) is focused on a focusing plane of the optical recording medium (c), and a coil (b6) which is wound in a groove (b5) provided at the light path opening portion (b3) on the optical recording medium (c) side of the air slider (b1) and forms a magnetic field that is approximately normal to the focusing plane of the optical recording medium (c). The floating head (b) is provided near the optical recording medium (c) and is supported by a spring-type suspension (b7) which can be moved radially with respect to the optical recording medium (c) by a drive unit (e).
This flying head (b) offers the advantage of being very light. One can aim for shortening access times since its structure is one in which only the smallest of elements such as the prism (b2), object lens (b4) and coil (b6), etc. are carried on the air slider (b1). There is the further advantage that since the structure is one in which the air slider (b1) can be floated by tho air stream that accompanies rotation of the optical recording medium (c), it is possible to keep the distance between the optical recording medium (c) and the object lens (b4) constant. Hence it is possible to dispense with an object lens (b4) focusing device.
However, since the overall structure of the air slider (b1) in this flying head (b) is comprised of the soft magnetic material, as noted above, the magnetic field that is generated by charging the coil (b6) with electricity is liable to be formed not just in the region on the light path opening portion (b3) side but also in the region outside the air slider (b1). Therefore, it is difficult to concentrate a vertical magnetic field directed to a set focusing plane of the optical recording medium (c), as illustrated in FIG. 23.
It is therefore necessary to provide an extremely large magnetomotive force in order to form a magnetic field of 200-300 Oe that is needed for magneto-optical recording or erasure on the focusing plane of the optical recording medium (c). The measure taken in the past to meet this requirement has been to increase the number of turns of the coil (b6).
However, it has been found that increasing the number of turns of the coil (b6) also results in an increase in self-inductance. Consequently it becomes impossible to effect high-speed switching of the direction of magnetic fields during information recording. Therefore, recording and overwriting speeds become slower.
Japanese Laid-open Patent Application No. 61-71437 discloses an improvement that is designed to effect focusing of a vertical magnetic field by the provision of a soft magnetic layer on the underside of the recording film of the optical recording medium and the formation of a magnetic path between this soft magnetic layer and the coil. This improvement is still insufficient, since it is unable to weaken the intensity of the magnetic field formed in the region outside the air slider (b1).